C/ctype.h/toupper
toupper: returns the uppercase equivalent of ch if ch is a letter or ch is returned unchanged
//Declaration: int toupper(int ch);
//Function: returns the uppercase equivalent of ch if ch is a letter or ch is returned unchanged.
#include <ctype.h>
#include <stdio.h>
int main(void){
putchar(toupper("a"));
}
/*
A*/